Generally speaking, in magnetic tape cartridges used as external storage medium for data backup of computers and the likes, a single reel wound with a magnetic tape is housed in a flat square-like cartridge case, which is composed of the lower half section and the upper half section. When a magnetic tape cartridge is used, the tape loading mechanism of a record playback unit extracts the magnetic tape from the cartridge case and winds it around the reel placed in the record playback unit, thereby running the magnetic tape. It explains why an opening, which is for extracting the leading end of tape, is provided on the side of the cartridge case that houses a single reel of this type. This opening is normally closed to protect against the dust, and opened by the tape loading mechanism of a record playback unit only when either recording or playback is performed by the record playback unit.
Of the magnetic tape cartridges mentioned above, the magnetic tape cartridge represented by LTO (Linear Tape Open) standard is so arranged that the sliding door, which slides along inside the side wall of the cartridge case, opens or closes the opening. The sliding door is capable of sliding smoothly fitted in the guide channels, which are provided on both inner surfaces of the upper half section and the lower half section of the cartridge along their side walls. And a spring member imposes the force on the sliding door in the closing direction to close the opening except for the occasion when the magnetic tape cartridge is in use.
The assembly of the magnetic tape cartridge with a sliding door is performed in the following manner. The respective parts such as a reel and a claw for the protection of inadvertent erasing are set on the prescribed position of the lower half section, the spring member and the sliding door are inserted into the guide channel of the lower half section, and then the lower half section and the upper half section are mated. When the spring member is inserted into the guide channel, it is mounted compressed on the sliding door so as to impose the force on the sliding door in the closing direction.
However, before the lower half section and the upper half section are mated, the sliding door 102 is liable to lift from the guide channel 103 of the lower half section 105 by the force of the spring member 101 as shown in FIG. 29, since the spring member and the sliding door, which are inserted in the guide channel, are not restricted upward. Therefore, when the lower half section 105 and the upper half section are mated without any measures, there has been a problem that the sliding door 102 is not able to be inserted properly into the guide channel 103 of the lower half section or another guide channel of the upper half section (not shown).
Also before the lower half section and the upper half section are mated, the sliding door 102 inserted in the guide channel 103 is liable to fall in the opposite of the side wall 104, namely inside the cartridge case as shown with the arrow in FIG. 30, since the guide channel 103 of the lower half section 105 is carved shallow as shown in the figure. Therefore, there has been a problem, the same as described above, that the sliding door 102 is not able to be properly inserted into the guide channel 103 of the lower half section 105 or another guide channel of the upper half section (not shown).